Significant Accounting Policies, Cash, Cash Equivalents and Investments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	$ 59,488	$ 56,350
Gross unrealized gains	6	8
Gross unrealized losses	(20)	(8)
Fair value disclosure	59,474	56,350
Cash [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	13,164	11,116
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value disclosure	13,164	11,116
Money Market Funds [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	14,437	17,235
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value disclosure	14,437	17,235
Certificates of Deposit [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	1,160	1,880
Gross unrealized gains	0	0
Gross unrealized losses	0	(1)
Fair value disclosure	1,160	1,879
Commercial Paper [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	3,247	5,745
Gross unrealized gains	1	1
Gross unrealized losses	(1)	(1)
Fair value disclosure	3,247	5,745
Corporate notes and bonds [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	25,770	20,172
Gross unrealized gains	5	7
Gross unrealized losses	(19)	(6)
Fair value disclosure	25,756	20,173
Municipal Securities [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	201
Gross unrealized gains	0
Gross unrealized losses	0
Fair value disclosure	201
US government agencies securities [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	1,509	202
Gross unrealized gains	0	0
Gross unrealized losses	0	0
Fair value disclosure	1,509	202
Cash and cash equivalents [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	29,753	30,853
Gross unrealized gains	0	0
Gross unrealized losses	0	(1)
Fair value disclosure	29,753	30,852
Short-term investments [Member]
Cash and Cash Equivalents and Investments [Line Items]
Amortized cost	29,735	25,497
Gross unrealized gains	6	8
Gross unrealized losses	(20)	(7)
Fair value disclosure	$ 29,721	$ 25,498